The invention relates generally to actuating devices, and more specifically to such devices having an axially-extending elongated actuating shaft that is rotatable about an axis and linearly movable along said axis in order to impart rotary and linear movement to another member or assembly.
Various rotary and linear actuating devices have been provided for imparting both rotary and linear movement to an external member. Such devices frequently include a rod or other member rotatably driven by a rack and pinion gear assembly that transforms linear motion to rotary motion. The rack and pinion assembly is in turn actuated by a pneumatic or hydraulic cylinder. One end of such a rotatable rod member is typically interconnected with another pneumatic or hydraulic cylinder for linear movement along the rod member's axis of rotation. An example of such prior devices is disclosed in U.S. Pat. No. 4,186,911.
Frequently, however, such previous devices are not well-suited for automated applications in point-to-point robot devices requiring precise actuation and positioning of a movable arm assembly used to lift heavy parts and reposition them in a very precise location. Such prior devices often include linear bearing assemblies that do not adequately support a heavy load on the arm assembly for precision movement thereof when the rod member is fully extended. Additionally, such prior devices frequently have too much clearance or backlash between the rod member and the linear bearings to allow for the required precision placement of parts or other items being transferred by the arm assembly, and typically do not have means for adjusting the amount of said clearance to accommodate wear in the mechanism.
In accordance with the present invention, an actuating device includes a rotatable assembly disposed for rotation about an axis within a housing. At least a portion of the rotatable assembly and the housing are radially spaced apart to define a fluid chamber therein, with means for varying the fluid pressure within the fluid pressure chamber in order to selectively vary the rotary position of the rotatable assembly relative to the housing. The rotatable assembly also includes an elongated member extending coaxially therethrough and preferably adapted to be secured to an external member that is to be actuated by the actuating device. The elongated member is preferably movable linearly along the axis of rotation of the rotatable assembly but is restrained for rotation with the rotatable assembly.
In a preferred embodiment of the present invention, the rotatable assembly has at least one radially-extending vane or blade member secured for rotational movement therewith in slidable and sealing engagement with the inside wall of the housing. The housing includes at least one radially-extending fixed vane or blade member protruding therefrom to slidably and sealingly engage the rotatable assembly. The rotatable and fixed vane members separate the generally annular space between the rotatable assembly and the housing into at least a pair of fluid pressure chambers. Thus the relative pressures in the fluid pressure chambers may be selectively varied in order to vary the rotary position of the rotatable assembly and the elongated member.
In a preferred form of the invention, the rotatable assembly also preferably includes a rotatable sleeve member having a substantially coaxial opening extending therethrough. At least a pair of generally cylindrical linear bearing assemblies are received within opposite ends of the opening in the rotatable assembly and are connected for rotation therewith. The elongated member is preferably carried within the linear bearing assemblies by means of a ball spline connection such that the elongated member is rotationally restrained relative to the linear bearing assemblies and the rotatable assembly, but linearly movable along the rotational axis of the rotatable assembly. The generally cylindrical linear bearing assemblies may be slightly rotated in opposite directions before being secured for rotation with the rotatable assembly, thereby allowing the clearance in the linear bearing assembly to be adjusted.
Additional advantages and features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the acompanying drawings.